Electron discharge cathode



Oct. 1l, 1932. 1 -loNEs ELECTRON DISCHARGE CATHODE Filed Feb. 28. 1929oxxDE EMU-TER coATnNG (la) ELECTRO-PLATED OUTER SHELL (H) CENTRAL COREor- METAL l(to) lNVENToR Lesfer 1 Jon es RNEYS Patented Oct. 11, 1932ffUNr LESTER L. JONES, F ORADELL, NEW ERSEY :ernennen Dieci-:meencnrnonn Application led February 28, 1929. Serial No. 343,255.

This invention relates to electron discharge devices or tubes and hasspecial reference to the provision of a novel cathode structure forelectron discharge devices or tubes.

The problem of constructing cathode elements embodying heaters for theoxide emitters in Velectron Vdischarge tubes has been fraught with manydifficulties and has led to severe limitations in the design of electron2 discharge devices or vacuum tubes. It is def slrable, for'eizample, tocoat the thermionicallyactive material or oxide emitter on a metal suchas nickel, molybdenum or tungsten.

V' [lhejresistanc'es ofthese metals are too low,

however, to generate the required amount of heatinthe current andvoltage ranges desirable unless the metal be Vdrawn into eX- tremelyfine wire, or unless long lengths be used. The drawing of thesemetals'into filamentsgives rise to the necessity for providing filamentsupporting structures to prevent the sagging and vibrational motions ofthe iine filaments and such filament supporting structures undesirablyoccupy considerable space in the vacuum tube.

Where thecathodes are of the so-called uni-potential heated type, it'hasbeen necessary to provide a considerable mass of insulating materialbetween the heater and the electron emitting cathode surface, the heatercomprising vin such uni-potential cathode structures an elementelectrically distinct from the electron emitting cathode surface. Thistype of uni-potential cathode gives rise to heater burnouts and isespecially troublesome in the construction' of relay tubes for broadcastreceivers due tothe relatively long time required to heat up the cathodeto the emitting temperature. y

In the construction of electron discharge tubes in which the heaters areenergized by alternating current, another problem resides in theimportance of confining the electrostaticfield due to the voltages inthe heater into a region outsi de the path of the electron flow. It isalso important to minimize the magnetic field due to the heater currentsespecially in the region of the electron current flow.

The prime desideratum of my present invention centers about theprovision of a new cathode structure in which the above disadvantagesincident either to the filamentary or indirectly heated prior art typesof cathode structures lare edectively obviated and which ischaracterized by new advantages and by the opening up of a new field ofdesign in the electron discharge tube and allied arts. Amongthese newadvantages which comprise objects of the present invention are the con-0U struction of acathode element including a heater which defines arigid self-supporting structure devoid of any insulating material, thefurther provision of a heater which is eX- tremely compact andpreferably of a long cylindrical form, the further provision of a heaterin which all of the parts are mechanically integral, are in intimateContact with one another and therefore free from any loose parts, thestill further provision of a cathode heater in which the heatdistribution is uniform tothe surface of application, and theconstruction of a heater in which the magnetic and capacitive fieldsldue to the heater n current and voltage are at a minimum. Theseadvantages and the accomplishments of these objects lead to importantresults in many fields; and in the present application I will relate theespecial advantages which appertain to the production of cathodes foruse in electron discharge devices or vacuum tubes. -To theaccomplishment of the foregoing and such other objects as willhereinafter appear, my invention consists in the elements and theirrelation one to the other, as herein- 8 afterv more particularlydescribed and sought to be dened in the claims; reference being had tothe accompanying drawing which shows the preferred embodiments of myinvention, and in which:

' Fig. l is a circuit diagrammatic view of an electron discharge deviceembodying my invention and showing one manner of its use:

Fig. 2 is a generalized structural view of an electron discharge tubeshowing my invention applied thereto; and

Fig. 3 is a view taken on an enlarged scale and showing in detail thecathode structure nf the present invention.

Having reference now more in detail to 10 resistance layer. Due lto thisConstruction,

the drawing and referring first.. to lFig. 3 thereof, the cathodestructure of the invention comprises a unitary element embodying spacedconduct-ing electrodes 10 and 11, one o-f which provides the electronemitting surface and a resistor element l12 defining the V heaterdisposed between and conductively inter-gral with .the electrodes 10 and11. VIn the preferred embodiment of the invention, theV electrode 10comprises a Vfairly rigid central core made, forexample,kofcopper,niclel, tungsten, etc., having a diameter approximately 1/100vof its length, the 4resistorv'element 12 comprises a coating of a highresistance material coated over and covering the core :10, andtheelectrode 11 comprises a conductive 'fllm'of such-a metal as silver,copper or nickel which` preferably .is electroplated over theresista-nce coatingV 12 and forms a cylindrical shell Whichreceivestheouter lcoating 13 of .a thermionically active preparation or oxideemitter.

In the design and construction of 'this cathodefelementitiscontemplatedythat the conductivity ofthe core 10 and of the electro-`plated shell 11 be yvery .high as compared 'to the conductivity oftherresistance layer or coating'` 12 therebetween. Heat is lthereforegenerated vin the' resistance Alayerland substantially the entirey.voltage dropy 'occurs in Vfthe the electrostaticr field incident-tothe heater voltage is thereforeconfined lto Within the heater elementand therefore toa Vregion out.- side the path of theelectron flow. Ifthe current be led in and :from the electrodes 10 and Y 11 by vmeansofthe conductors 141: and 15fat-` tached to the electrodes, as shownin'Fig. 3

Y of the drawing, substantially no magnetic field is created vbecausethereturn current is ledba-ck to the point oforigin along the path inextremelyclose spacial relationship to the outgoing path. Thus themagnetic field due to theheater currents is minimized especially in theregionof the electronY current flow. It Will also be noted thatthat partof thefcurrent Which is used for heating near the heater terminals doesnot travel through .themore remote portions of the heater, and thereforethe-remote portions have lesser currents and thefresidual'magneticfield' intheir. vicinity ode unitsor heatersof the prior art. Theconstructionof a self-supportingtheater in this fashion gives rise to aminimum of miaterial to be heated and therefore to extremely fastheating of the cathode and permits the '-taryltypes ofscathodeof theprior art. The

compacting of the cathode confining the same into a minimum of space,permits ofthe use of muchV smaller grids `and plates with consequentadvantages in the reduction of interelectrode capacities vof theelectron discharge device. All ofthe parts of theheater .beingconductively integral are in intimate contact, and `therefore lthe unitas Ia Whole 1s free from any looseparts. lIt will be apparent, moreover,that the heat distributionris uniformto thesurface ofapplication,

In lthe preferred construction, `the resistor element 12 comprises lahigh resistance .material of the kind described vandfclaimed inthe'application of Lester L. Jones, et al.,

Serial No.167,588, 'filed February 1927, and theelectroplatedouterjshell 11,1sapplied to` the resistor coating 12 preferablym themanner described and claimed in the ,application ofjLester LJones andJoseph A. Flanzer, SerialNo'. 260,987, filed March v12, 1928.set-'forthvinsaid application, V.the resistance coating 12 is composed,ofa finely divided graphite mixed With a binder .and vehicle consistingof a `metallic phosphate. In compounding, they resist-ance material, thegraphite, preferably a colloidal graphite, is vmixed With a solution ofaluminum in phosphoric acid to form a. freely flowing paint. AThealuminum in the phosphoric acid produces an aluminum phosphate; and intheY preparation Vof the aluminuml .phosphate it has been founddesirable .to Aadd aluminum to the phosphoric acid in such ,an amount asjust fails to produce :a precipitate. Addition'of ymore than thisamount, Which would .produce .a precipitate, is .undesirable because'ofthe-presence inthe paint of large particles Yformed bythe precipitateWhichinterferevvith the productionof a smooth uniform tilm.' On theother hand, the addition ofan insufficient quantity of aluminum .oraluminum phosphate is .undesirablemainly because -of theumore highly*kacid condition of the resulting paint, Which tends to destroy thecolloidal knature of the graphite, cause ing clotting of the paint Withstreahiness in the film. It kis therefore .preferred pto. use a solution.of aluminum in phosphoric acid in a slight excess 4of phosphoric acid,aluminum being added'v in suchan amountas just fails'toproduce aprecipitate. y'The aluminum phosphate may also be preparedfby theaddition 4of C. vAP...aluminum phosphate to phosphoric acid insuiiicient quantity to just copper or nickel. 15

avoid the formation of any precipitate.

The paint thus compounded is then applied to the conductive core 10 bymeans of a brush or by dipping or by any other method. After beingapplied the embryo unit thus formed is subjected to a heat treatmentwhich produces a tough and durable coating or film having a relativelyhigh resistance. This coating (12) is thenelectroplated to the requiredthickness, usually of the order of several thousandths of an inch ofconducting metal which may be silver, The paint coating 12 is found toadhere very firmly to the conductive core 10 and forms a firm basis orsupport for the deposited or plated metal film. In afixing the terminals14- and 15 to the electrodes of the cathode unit, it is preferred toreinforce one end of the electrode shell 11 with a ring 16 of additionalthickness and this may be accomplished by the method of spotelectroplating the shell 11, as kkdescribed and claimed in the copendingapplication of Joseph A. Flanzer, Serial No. 228,-

264, led October 1, 1927. The lead wires or conductors 14 andl may thenbe spot welded, one to the end of the core 1() and the other to thereinforced spot plated ring 16. In some 'cases the reinforcement may beplaced at the middle of the heater instead of at one end thereof. l

In F ig. 2 of the drawing, I show diagrammatically the structuralinter-relation between the cathode unit of my invention and the otherelements of an electron discharge device illustrating some of theadvantages hereinbefore outlined when the heater is used in an electrondischarge tube. This electron discharge device comprises the usualevacuated vessell 17 provided with the cathode C of the presentinvention, the said cathode being surrounded by the grid structure Grwhich is interposed between the cathode and the plate P.

In F ig. 1 of the drawing, I show diagrammatically a vacuum tubeembodying the cathode of the present invention depicting the manner ofconnecting such a vacuum tube in a relay circuit.v As shown, theelectrodes 10 and 11 of the cathode unit are connected to a battery A,the electrode 11 and the grid Gr comprising the electrodes of an inputcircuit I which is fed from a transformer T, said input circuit beingprovided, for example, with a battery C. The electrode 11 and the plateP form the electrodes of an output circuit O which in turn is connectedto a transformer T', and which output circuit is supplied with a batteryB. The use and operation of such amplifier or relay circuits, as shownin Fig. 1 of the drawf ing, is well known to the art and need not befurther detailed. c

The manner of making cathodes or heaters of the present invention andthe making of electron discharge devices embodying such cathodes orheaters, and the many advantages in the manufacture and use thereof willin the main be fully apparent from the above detailed descriptionthereof. It will be further apparent that while I have shown anddescribed my invention in the preferred forms, many changes andmodifications may be kmade in the structure disclosed without departingfrom the spirit of the invention, defined in the following claims. i

I claim:

, 1. kA heater comprising a conductive core, aiconductive shell havingone closed end and surrounding said core, a resistor element disposedbetween and forming the sole conductive path between said core andshell, and lead-in wires connected to the core and the shell at one endonly of the said heater.

2. A unitary heater structure comprising a rigid highly conductivemetallic core and support, a thin film or coating of high resistancematerial over said core, a highly conductive film of metal over said`resistance coating, the resistance film forming the sole conductive pathbetween the support and the metallic film, an electron emitter coatingover said film, and lead-in wires connecten"- to the metallic core andthe metallic film at one end only of said heater.

3. An electron emitting cathode comprising a conductive core definingone cathode electrode, a resistor coating thereon forming the cathodeheater, and a conductive shell having one closed end surrounding saidresistor coating and defining the other cathode electrode, said resistorforming the sole conductive path between the core and the shell.

4. A unit-potential cathode for low powered electron emission tubescomprising a central highly conductive wire or rod, a thin heaterresistance surrounding the rod, a thin highly conductive metallic shellsurrounding the heater resistance, the resistance material forming thesole conductive path between the rod and the shell, and lead-in wiresconnected to the rod and the shell at one end only of said rod and shellwhereby a selfsupporting rigid cathode is provided having a smalldiameter and small mass for low heat radiation loss and quick heating.

5. A cathode for low powered electron emission tubes comprising a highlyconductive wire or rod, a high resistance film coated on the rod, ahighly conductive metallic shell plated over the resulting resistancecoating, the resistance material forming the sole conductive pathbetween the rod and the shell, a thermionically active material appliedto the said metallic shell, and lead-in wires connected to the rod andthe shell at one end only of said rod and shell.

6. A uni-potential cathode for low powered electron emission tubescomprising a y central highly conductive wire or rod, a carly bona'ceoushigh resistanceilm coated on the rod7` a'highly conductive metallicshell plated;

y. over theV resulting resista-nce film, the resista ance materialformingjthe sole 'conductive path between the rod and the'shell, ather.-`

In'ionically activematerial applied to the said metallic shell, andlead-in WiresV connected Il, to the rod and the shell at one end only ofi saidfrod and shell, wherebya self-supportf ing rigid cathodeis'provided having, a small diameter and small mass lor low heatradiay'tion loss and quick heating. f

' 7. *Acathod'e comprising a highly` conducg tive wire or rod, a heaterresistance surround ing the walls and one end of the rod, and4 a highlyconductive metallic shell placed over the' walls and end of the heaterresist- K. ance, said resistance being in intimate con- 0 tact with saidconductors and forming an electricalv path therebetween.

' 8. A cathode for low powered electron Y emission tubes comprising ahighlycon'ductive wire or rod7 a highl resistance film coated entirelyaround the walls and one fend of the rod, a highly conductive metallicshellplated onthe walls and end of 'the resulting resistance coating,and a therinionically active inaterial applied to the said metallicshell.v-

' `9. A cathode for low powered Yelectron emission tubesV comprising ahighly conductivewire or rod, a carbonaceous high resist'- ance film"coated entirely VaroundA the walls ,4 and one Ae'ndof the rod, and ahighly conduc- A tive metallic shell plated on the walls and end of theresulting resistance coating. Y

10. A non-magneti uni-potential cathode for' low powered electronemission tubes com- 4 prising a central highly conductive wire or V23;()rod, a carbonaceous high resistance Vfilm coated entirely aroundthewalls and one end of the rod, a highly conductive metallic shell platedon the walls and end of the "resulting resistancecoating;and athermionically active material applied to the said metallic shell,ywhereby a self-supporting rigid cathrode is provided having a smalldiameter and small mass for low heat radiation loss ,andy

`. quick heating.V l

` Signed at New York in the county of New York and VState of New Yorkthis 26th day of February A. 1929.

i LESTER L. JONES.

